The present invention relates to switch assemblies incorporating microswitches, and to methods of making same.
Various embodiments for microswitches and switches incorporating resilient membranes have already been disclosed in the prior art.
In particular, DE 196 53 322 A1, depicts, as seen in FIG. 1 of the document, a microswitch defining a contact space 6 formed between a glass substrate 2 and a silicon membrane 4. Electric contacts 7, 8 and 9 are provided on opposite inner sides 2a and 3c of the substrate 2 and the silicon membrane, and contact conductors 10 and 11 are led out of the contact space. A single contact is provided on the inside of the silicon membrane as a contact bridge 9. Additionally, two separate fixed contacts 7 and 8 are connected with the contact conductors on the inside of the substrate as contact partners for the contact bridge, the contact space being preferably hermetically sealed.
It is generally known in the art that the glass disc and silicon membrane may be permanently fused to each other by anodic bonding and form a completely sealed switch area in which two gold plated contacts are located. The silicon disc may be thinned to a few 10 micrometers over a cavity and serves as the surface for receiving the switching pressure. In the event of external loading, the silicon membrane deforms to allow both contacts to touch, thereby closing the circuit.
U.S. Pat. No. 5,399,821 pertains to a push-button keytop switch. The switch is formed by deforming a flexible resin film such that it bulges upwardly to form a curved portion, and thereafter filling the curved portion with a molding resin. The molding resin is allowed to harden to form a keytop body. The keytop is manufactured by clamping a resin film between upper and lower molds, charging a resin from a pin gate into a cavity provided in the lower mold, thereby deforming and urging the resin film upward by pressure and heat produced by the resin and causing the resin film to adhere to the inner surface of the upper mold. The cavities of the upper and lower molds are filled with the resin, and the molds are separated after the resin hardens.
DE 34 47 085 C2 discloses a push-button switch with an elastic membrane made of rubber-like elastic material such as from elastic rubber, synthetic rubber, or plastic material as the actuating element. The switch exhibits reliable closing of the contacts with a low intrinsic resistance. As seen on FIGS. 1a and 1b, the membrane has an operating ring 21 acting on the contact link 14 for closing the contact, ring 21 being plastically deformable.
DE 43 35 246 A1 discloses a push button switch and manufacturing process that has a moving contact at push-button 14 and fixed contacts 12. Push-button 14 incorporates a flexible membrane portion at sides thereof which allow a depression of 14 for closing the circuit through touching of the moving and fixed contacts.
Microswitches as disclosed above have the advantage of providing a space saving alternative to regular switches, thereby accommodating the corresponding reduction in size of electronic circuits they are meant to complement. Moreover, microswitches typically provide exact and constant switching points, low contact erosion, constant resistance, and mechanical stability. In addition, switches incorporating mechanically compliant or resilient membranes such as those made of silicon advantageously allow the repeated application of actuation pressures without resulting in fatigue. At the same time, actuation membranes can be provided so as to allow the microswitch and/or switch to exhibit desirable moisture and dust proof properties, further defining a hermetic encapsulation with the possibility of maintaining predetermined microclimates therein. The use of microswitches incorporating resilient membranes can thereby result in an altogether more reliable and cost-effective product for machines, equipment controls, keyboards and other such applications.
While microswitch and membrane switch structures are known, mounting techniques for mounting microswitches in assemblies for further integration into various switching processes have not been fully explored.
An object of the invention is to provide a method for mounting microswitches of the type initially cited which preserves the advantages associated with the microswitch while permitting the microswitch to be integrated in further switching processes in a reliable, cost effective, space-saving manner. Another object of the invention is to provide a microswitch module resulting from the practice of the above method.
The above objects of the invention, and other objects to become apparent as the description progresses, is achieved by providing a method of making a microswitch module comprising the steps of: charging a resin onto a loading surface of a microswitch; disposing an actuator element onto the resin charged onto the loading surface of the microswitch; and ensuring that the actuator element remains fixed while at least part of the resin hardens into a layer of resilient material thereby providing a microswitch module wherein the actuator element is adapted to transmit a mechanical switching force to the loading surface of the microswitch through the layer of resilient material for actuating the microswitch. Advantageously, the above method may include the steps of providing a microswitch housing and disposing the microswitch in a cavity defined by the microswitch housing.
According to one embodiment, the step of disposing the microswitch includes the step of bonding the microswitch to a cavity surface of the cavity defined by the microswitch housing, where the bonding step comprises the steps of charging a liquid adhesive onto the cavity surface; disposing the microswitch onto the liquid adhesive on the cavity surface; and allowing the liquid adhesive to harden.
Additionally, the step of ensuring may further include the step of holding the actuator element in a fixed position onto the dosed amount resin while the resin is hardening, and/or of ascertaining a provision of a pre-determined thickness of the layer of resilient material after hardening of the resin. In the latter case, the actuator element may be pushed onto the resin charged onto the loading surface of the microswitch such that the resin partially migrates to lateral regions of the actuator element.
According to one advantageous embodiment, the step of ensuring further includes the step of holding the actuator element in a fixed position onto the resin charged onto the loading surface of the microswitch such that a top surface of the actuator element is in registration with a top surface of the microswitch housing.
In addition to holding the actuator element in a fixed position with regard to the microswitch housing, the resin fulfills the function of compensating for production tolerances of the actuator element, the microswitch and the microswitch housing. For example, the provision of a top surface of the actuator element being in registration with a top surface of the microswitch housing will for each microswitch module, depending on the specific tolerances of the actuator element, the microswitch and the microswitch housing, result in a different spacing between a bottom surface of the actuator element and a top surface of the microswitch. This variance may be compensated by the thickness of the layer of resin that is formed between the two surfaces when the resin hardens.
The objects of the invention are further achieved through the provision of a microswitch module comprising a microswitch; a layer of resilient material disposed on a loading surface of the microswitch; and an actuator element disposed on the layer of resilient material for transmitting a mechanical switching force therethrough to the loading surface of the microswitch for actuating the microswitch. The module may further comprise a microswitch housing defining a cavity therein, the microswitch being disposed in the cavity of the microswitch housing. The microswitch may further be bonded to a cavity surface of the cavity of the microswitch housing.
In one advantageous embodiment, the actuator element is in registration with a top surface of the microswitch housing.
The invention further includes within its scope the provision of a module housing for receiving therein a switching module. The module may be according to one of the above embodiments. The module housing comprises an outer shell defining a module housing cavity.
Additionally, the invention pertains to a combination comprising the module according to one of the above embodiments and further the module housing which houses the module therein.
The invention further pertains to a switching system that includes a module disposed in a module housing, and further comprises a loading spring secured to the module housing. The module and module housing may be according to one of the embodiments described above. According to one embodiment of the switching system, the loading spring may comprise either a bent resilient sheet having a loading portion thereon or a telescoping spring-biased actuator.
Additionally, the invention pertains to a combination comprising the switching system according to one of the embodiments described above, and further including an actuating mechanism disposed adjacent the switching system for applying a mechanical load to the loading spring thereof for actuating the microswitch of the module. According to one embodiment, the actuating mechanism comprises one of a rotatable cam, a hinged lever and a cover that is one of translationally and rotationally movable by a predetermined distance.
The invention further comprises within its scope a combination comprising the module and the module housing according to one of the embodiments described above and further including an actuating mechanism disposed adjacent the module for applying a mechanical load thereto for actuating the microswitch. Advantageously, the actuating mechanism comprises a rotatable disc housing a spring-biased ball therein.